As the demand for electronic and photonic devices grows, the need to reduce the cost of producing such devices for existing applications, such as computation, communications, electronics and displays, as well as for new applications, also grows.
Much of the cost of electronic devices is related to the processing steps needed to formulate the devices, rather than the materials costs. In large area applications, where arrays of thin-film transistors are employed, the costs associated with traditional processing methods can become particularly important.
Organic thin-film transistors have been and are being developed as low-cost alternatives to traditional inorganic semiconductors. In particular, organic semiconductors have been investigated for use in thin-film transistors, particularly in low-performance, large-area applications, such as liquid-crystal displays and electric paper, as well as in light-emitting diodes and photovoltaics. Organic semiconductors are also being investigated as alternatives to traditional inorganic materials for use as circuitry for plastics-based devices, because of their potential for lowering processing costs and for their compatibility with low-temperature processes.
Organic semiconductors can be processed into organic thin-film transistors at relatively low costs. Because organic semiconductors tend to be soluble and easily form continuous films, techniques such as jet printing, screen printing, micromolding and spin-coating followed by photolithography can all be used to fabricate patterned thin-film transistors using organic semiconductors, unlike traditional inorganic semiconductors.
For example, WO 02/084758 A1 discloses phase separation of polymer blends in relation to optoelectronic devices, and phase separation for encapsulation of thin-film transistors has also been studied and disclosed in copending U.S. Patent Application entitled “Method for Forming a Bottom Gate Thin Film Transistor Using a Blend Solution to Form a Semiconducting Layer and an Insulating Layer,” filed Jun. 24, 2004 Ser. No. 10/876,229. Spontaneous dewetting of a semiconductor solution, for device array fabrication is described in M. L. Chabinyc et al., “Organic Polymer Thin-Film Transistors Fabricated By Selective Dewetting,” Applied Physics Letters, 81, 4260 (2002). The disclosures of WO 02/084758 A1 and Chabinyc are incorporated herein by reference in their entireties.
C. R. Kagan et al., “Patterning Organic-Inorganic Thin-Film Transistors Using Microcontact Printed Templates,” Applied Physics Letters 79(21) 3536 (2001), the disclosure of which is incorporated herein by reference in its entirety, discloses that patterned, solution-deposited, organic and inorganic thin-film transistors can be prepared by a low cost, low temperature process. The thin-film transistors of Kagan are produced by flooding a surface patterned with hydrophilic and hydrophobic regions with a thin-film precursor that selectively deposits on regions of like wettability.
In addition, lateral phase separation of polymer blends has been achieved on patterned substrates, for example, as disclosed in U.S. Pat. No. 6,391,217 and in Martin Böltau et al., “Surface-Induced Structure Formation of Polymer Blends on Patterned Substrates,” Nature 391, 877 (1998), the disclosures of each of these references are incorporated herein in their entireties. In U.S. Pat. No. 6,391,217, polymer blends are deposited on a surface and lateral phase separation is patterned by application of an electric field, while Böltau discloses a method in which polymer blends laterally phase separate based on the patterned surface energy of the substrate.
In addition, the formation of phase-separated layers is known for block copolymers, and such phase separation can be driven by variations in the surface energy of the substrate on which the block copolymers are deposited. This can be seen, for example, in Kim et al. “Epitaxial Self-Assembly of Block-Copolymers on Lithographically Defined Nanopatterned Surfaces,” Nature 424, 411 (2003) and in U.S. Pat. No. 6,746,825, the disclosures of each of these references are incorporated herein by reference in their entireties.
Surface energy patterning has also been shown to be effective to pattern metal contacts from nanoparticle solutions for semiconductor devices, as disclosed in Ando et al., “Organic Thin-Film Transistors Fabricated with Alignment-Free Printing Technique,” Materials Research Society Proceedings, 110.19.1 (Spring 2004), the disclosure of which is incorporated herein by reference in their entireties. In Ando, a semiconductor is deposited on a substrate in a blanket layer from a single component solution or from vapor phase.
Conventional techniques require additional processing to encapsulate and/or isolate single devices. Thin-film transistors can be prepared by a combination of additive processes, such as such as ink-jet printing, screen printing, digital printing, micromolding and spin-coating, and subtractive processes, such as digital lithography and conventional photolithography. In these techniques, separate processing steps are still required to encapsulate and/or isolate single devices.
In particular, there remains a need for processes for preparing thin-film transistors in which semiconductor materials can be patterned and both encapsulated and isolated by insulating materials in a single step.